Once again solid and good. The bishop is moving out of the opponent's attack to a better square, protecting the kingside in the process.
17. e2d3  17... b8c8 The opening is a success for Black. He has managed to trade a pair of minor pieces—always a good thing in the ensuing battle with the isolated/hanging pair of pawns. 18. e1g1  18... e8g8  19. c3c4 Carlsen takes the chance to modify the pawn structure to \"hanging pawns.\" From the isolani family, this is considered the most beneficial relative.